1. Field of the Invention
The present invention relates to: an amplification-type solid-state image capturing apparatus having an amplification function for amplifying and reading signal charge, into which light of a subject is photoelectrically converted by a photoelectric conversion element; and an electronic information device using the amplification-type solid-state image capturing apparatus for an image capturing section thereof, and in particular, the present invention relates to: an amplification-type solid-state image capturing apparatus, in which a charge detection section is shared by a plurality of pixel sections; and an electronic information device (e.g., digital camera (digital video camera, digital still camera), image input camera, scanner, facsimile, cell phone device equipped with camera and the like) using the amplification-type solid-state image capturing apparatus as an image input device for an image capturing section thereof.
2. Description of the Related Art
Generally, as a conventional amplification-type solid-state image capturing apparatus, an amplification-type solid-state image capturing apparatus is widely used, which includes a pixel section having a function for amplifying signal charge and a scan circuit arranged around the pixel section, and which is configured to read pixel data from the pixel section by the scan circuit.
As an example of such an amplification-type solid-state image capturing apparatus, an APS (Active Pixel Sensor) image sensor is known, which is configured by a CMOS (Complementary Metal Oxide Semiconductor). As a common CMOS APS image sensor, a three-transistor type or four-transistor type CMOS APS image sensor having a predetermined number of transistors in each pixel is known. Among them, a four-transistor type CMOS APS image sensor which can obtain a high quality image has been recently becoming a mainstream.
Hereinafter, an exemplary structure of a pixel section in a conventional four-transistor type APS image sensor will be described in detail with reference to FIG. 7.
FIG. 7 is a circuit diagram showing an exemplary structure of a pixel section in a four-transistor type APS image sensor including four MOS transistors in the pixel section.
In FIG. 7, each pixel section in the conventional APS image sensor includes: a photoelectric conversion element PD; a transfer transistor T1 for transferring signal charge from the photoelectric conversion element PD to a charge detection section FD; an amplification transistor T2 for amplifying and reading potential at the charge detection section FD; a reset transistor T3 for resetting the potential at the charge detection section FD to a power supply voltage Vdd; and a selection transistor T4 for selectively reading an output from the amplification transistor T2 to a reading signal line SIG.
The transfer transistor T1 is connected between the photoelectric conversion element PD and the charge detection section FD. A gate of the transfer transistor T1 is connected to a transfer transistor drive line TX.
The amplification transistor T2 is connected between the power supply voltage Vdd and the selection transistor T4. A gate of the amplification transistor T2 is connected to the charge detection section FD.
The reset transistor T3 is connected between the power supply voltage Vdd and the charge detection section FD. A gate of the reset transistor T3 is connected to a reset transistor drive line RST.
The selection transistor T4 is connected between the amplification transistor T2 and the reading signal line SIG. A gate of the selection transistor T4 is connected to a selection transistor drive line SEL.
The reading signal line SIG is connected to a ground voltage end via a load transistor T5. A plurality of pixel sections is arranged in a matrix, and a plurality of reading signal lines SIG is provided in one direction.
The photoelectric conversion element PD is a light receiving section, and it is generally configured by an embedded photodiode and generates signal charge in accordance with an amount of incident light from an external subject.
With the structure described above, signal charge which has been photoelectrically converted by the photoelectric conversion element PD is transferred by the transfer transistor T1 from the photoelectric conversion element PD to the charge detection section FD.
At the charge detection section FD, prior to the transfer of signal charge from the photoelectric conversion element PD to the charge detection section FD, the potential at the charge detection section FD is reset to the power supply voltage Vdd by the reset transistor T3. Then, the transfer transistor T1 is placed on an on-state, and the signal charge is transferred from the photoelectric conversion element PD to the charge detection section FD.
Subsequent to the transfer of signal charge after the resetting, the potential at the charge detection section FD is amplified by the amplification transistor T2. The amplified potential is read as signal to the reading signal line SIG via the selection transistor T4. The read amplified potential is received by the load transistor T5 connected to the end of the reading signal line SIG so as to output a signal Vout.
A structure of one pixel section in the conventional amplification-type solid-state image capturing apparatus shown in FIG. 7 requires a plurality of transistors in the one pixel section. Therefore, it is difficult to reduce the size of a pixel. As such, a method is proposed, in which the average number of transistors in one pixel section is reduced by sharing transistors in the one pixel section by a plurality of photoelectric conversion elements.
As an example, Reference 1 proposes an amplification-type solid-state image capturing apparatus in which a charge detection section FD is shared by four photoelectric conversion elements PD adjacent to each other in a vertical direction.
Hereinafter, an exemplary structure of a pixel section in a conventional four-transistor type APS image sensor disclosed in Reference 1 will be described in detail with reference to FIG. 8.
FIG. 8 is a circuit diagram showing an exemplary structure of a pixel section in a conventional four-transistor type APS image sensor disclosed in Reference 1.
In the conventional APS image sensor in FIG. 8, four pixel sections are used as one unit, and each four-pixel section includes: four photoelectric conversion elements PD-1 to PD-4 adjacent to each other in a vertical direction; transfer transistors T1-1 to T1-4 each forming a pair with corresponding one of the photoelectric conversion elements PD-1 to PD-4; a charge detection section FD connected to an end of each of the transfer transistors T1-1 to T1-4 which is not connected to each of the respective photoelectric conversion elements PD-1 to PD-4; a reset transistor T3 for resetting potential at the charge detection section FD to a power supply voltage Vdd; an amplification transistor T2 for amplifying the potential at the charge detection section FD; a selection transistor T4 for selectively reading an output from the amplification transistor T2 to a reading signal line SIG.
With the structure described above, first, the reset transistor T3 is placed on an on-state, and the potential at the charge detection section FD is reset to the power supply voltage Vdd.
Then, the transfer transistor T1-1 located at the top is placed on an on-state, and signal charge is transferred from the photoelectric conversion element PD-1 to the charge detection section FD. The potential at the charge detection section FD having the difference resulting from before and after the operation of transferring signal charge is then amplified by the amplification transistor T2. Then, the amplified potential is read to the reading signal line SIG via the selection transistor T4.
Similarly, an operation of transferring signal charge to the charge detection section FD, an operation of amplifying the potential at the charge detection section FD having the difference resulting from before and after the operation of transferring signal charge and an operation of reading the amplified potential (signal) to the reading signal line SIG are subsequently performed for each of the photoelectric conversion element PD-2 located second from the top, the photoelectric conversion element PD-3 located third from the top and the photoelectric conversion element PD-4 located fourth from the top.
Next, the signal charge read to the reading signal line SIG is received by the load transistor T5 connected to the end of the reading signal line SIG so as to output a signal Vout.
Reference 1: Japanese Laid-Open Publication No. 2006-222427